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CBSE Class-1 Physics Quick Revision Notes Chapter-01: Electric Charges and Fields Like Charges and Unlike Charges: Like charges repel and unlike charges attract each other. Conductors and Insulators: Conductors allow movement of electric charge through them, insulators do not. Quantization of Electric Charge: It means that total charge (q) of a body is always an integral multiple of a basic quantum of charge (e) q=ne where n = 0, #1, +2, +3, .... Additivity of Electric Charges: Total charge of a system is the algebraic sum of all individual charges in the system. Conservation of Electric Charges: The total charge of an isolated system remains uncharged with time. Superposition Principle: It is the properties of forces with which two charges attract or repel each other are not affected by the presence of a third (or more) additional charge(s). The Electric Field E at a Point due to a Charge Configuration: It is the force on a small positive test charges q placed at the point divided by a magnitude lal Aner? \ It is radially outwards from q, if q is positive and radially \ inwards if q is negative. r \ E ata point varies inversely as the square of its distance \ from Q, the plot of £ versus r will look like the figure given below. Coulomb's Law: The mutual electrostatic force between two point charges qi and qz is proportional to the product qiq2 and inversely proportional to the square of the distance r21 separating them. Fn( force on q, due to q,) = Kaa), 21 Where rz: is a unit vector in the direction from qi to q2 and k = is the 0 proportionality constant. An Electric Field Line: It is a curve drawn in such a way that the tangent at each point on the curve gives the direction of electric field at that point. Material Downloaded From SUPERCOP Important Properties of Field Lines: These are: (i) Field lines are continuous curves without any breaks. (ii) Two field lines cannot cross each other. (iii) Electrostatic field lines start at positive charges and end at negative charges - they cannot form closed loops. Electric Field at a Point due to Charge q: g-£ q Electric Field due to an Electric Dipole in its Equatorial Plane at a Distance r from the Centre: =p 3 47€, (@+ry =? for >a TE, Electric Field due to an Electric Dipole on the Axis at a Distance r from the Centre: 2pr ~ 4ne, (1° -a’y Ter , for >a A Dipole Placed in Uniform Electric Field E experiences: Torque t, T= pxE The Electric Flux: g= fae = [Eds is a ‘dot’ product, hence it is scalar. Ag@ is positive for all values of 0 <4 Agis negative for all values of 0 >t Gauss’s Law: The flux of electric field through any closed surface S is 1/0 times the total charge enclosed by S. Bact =| Eds=— 9-JEds=— Electric field outside the charged shell is as though the total charge is concentrated at the centre. The same result is true for a solid sphere of uniform volume charge density. The electric field is zero at all points inside a charged shell. Material Downloaded From SUPERCOP 
